The chapter discusses areas of future research that might supplement some of the recommendations made in the previous chapter and improve the overall guidelines available on the topic.
From the data collected, it was observed that a total of 44 vehicles over the entire data collection period did not comply with the PTS unit in the absence of a flagger due to the extended wait time. To mitigate this issue of RLR due to excessive wait times, it was recommended to display the expected wait time with the help of an appropriate sign. This could be done in one of two ways. First, the contractor could install a portable dynamic changeable message sign that informed the drivers of the expected wait in real time. Also, these dynamic message signs could be synchronized with the PTS handheld remote control and an algorithm could be developed that provided the drivers with a more precise wait time. It could be effective in reducing the driver anxiety and minimize the urge to run the light due to extended wait times. It is KDOT policy that the long rural work zones in Kansas with pilot car operations avoid a pilot car round trip time more than 15 minutes. Thus, a second alternative to the dynamic message sign would be to install a static sign informing drivers of the total wait time. This would be a cheaper alternative and could be effective in reducing the noncompliance rates that occurred due to extended wait times. A scope for potential future research would be to conduct a study wherein noncompliance rates in presence of a static message sign or a dynamic changeable message sign could be compared with the noncompliance rates in their absence.
The volume thresholds designed and recommended in the research included all vehicle types, i.e., passenger cars, trucks, buses, RVs, and motorcycles. To determine the effects of the presence of a truck or a heavy vehicle in the queue, additional data need to be collected and additional analysis will need to be conducted in order to develop more in-depth equations and recommendations regarding signal timing operations.
Pilot car speeds were reduced close to the activity area by as much as 20 mph. The researcher was unable to accurately factor in the length of the activity area since it varied and no
were available. Additional research could be conducted to more precisely determine a speed reduction factor and incorporate it into the equation proposed in this research. Also, the turnaround times for the pilot car could be factored in the equation with the help of some additional data.
Additional research could also be conducted to determine the exact values of pilot car turnaround time and platoon clearance time and deduct them from the value of the maximum green interval obtained from the equations stated earlier.
Although it is unlikely that all the issues with the system can be addressed in a single research step, it will remain a worthy goal.
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Appendix A: Portable Traffic Signal (PTS) Specifications
Portable Traffic Signal (PTS)
Two ADDCO Galaxy PTS-2000 PTS systems were used for the research. Figure A.1 shows the two PTS units used for the research.
Figure A.1: Two PTS Units Used for the Study
As shown in Figure A.1, each trailer had a bank of batteries with solar recharging, two signal heads, and an integrated radio with solid state signal control and scaling redundant conflict monitoring system1. The PTS system was easy to transport, setup, operate, and take down at the end of the day. Technical details regarding the PTS unit relevant to the study are listed in the subsequent section. Figure A.2 shows a single, fully raised PTS unit.
1
GALAXY Procurement Specification: ADDCO Solar Portable Traffic Signal Trailer with Galaxy Operating
Figure A.2: A Fully Raised PTS Unit
Overall Dimensions
Deployment height: pavement to bottom of upper signal head = 17 feet Deployment height: pavement to bottom of lower signal head = 10 feet Height: PTS fully raised = 20 feet 4 inches to the top of the signal head Transport height: pavement to bottom of upper signal head = 9 feet 2 inches Transport height: pavement to bottom of lower signal head = 7 feet 11 inches Width: at the widest point = 8 feet 3 inches
Length: master trailer with hitch = 14 feet 5 inches Length: remote trailer with hitch = 12 feet 9 inches Length: in tandem tow configuration = 25 feet 4 inches Gross weight = 3,780 lbs. to 3,940 lbs.
Signal Heads Specifications
Figure A.3: PTS Signal Heads
1. Signal head LEDs were warranted for a 5-year life span.
2. Standard ITE approved polycarbonate 12-inch diameter signal heads. 3. There were two signal head assemblies per trailer standard. The outer
signal head was a permanent mount. The second may be quickly mounted by the user either over the roadway or at the lower position on the mast (factory shipped position).
4. The signal heads had the ability to be rotated 180 degrees to face in the opposite direction with a simple lockable spring loaded release mechanism. In addition, many horizontal and vertical adjustment positions were available to provide optimum visibility to the drivers.
5. Both signal heads had the ability to rotate and lock in 10-degree increments to position the signal head for the optimum visibility to the drivers.
6. Optional: (a) Aluminum signal heads, (b) Backing plates, (c) Units capable of being transported and operated with backing plates.
7. A work zone safety light was located on the rear side of the upper signal head. Its function was to alert workers of the traffic signal light status. The work zone safety light illuminates when the traffic signal status is “red.”
Batteries
Figure A.4 shows the batteries provided in a single PTS unit.
• Up to sixteen (16) 6 volt, 225 amp-hour deep cycle heavy duty batteries providing over 21 days continuous operation without solar array assist.
• Batteries are wired in a 12 VDC configuration.
Figure A.4: Batteries Provided (Source: Procurement Specifications PTS-2000)
Photo Voltaic Solar Array
Figure A.5 shows the photo voltaic solar array on a single PTS unit.
• Up to six panels ranging from 80-95 watts power produced per panel.
• A tilt and rotate system increases solar collection efficiency by allowing the panels to be optimally set for exposure to the sun.
Figure A.5: Tilt and Rotate System for the Solar Panels
Transmitter/Receiver Specifications
• Power Output: 10 mW -1 watt power output (up to 4 mile range)
• Frequency: ISM 902 - 928 MHz operating frequency
• Spread Spectrum: FHSS, frequency hopping spread spectrum
• Modulation: FSK frequency shift keying
Radio Remote Control
Figure A.6 shows the handheld remote control used to operate the PTS unit. 1. Electrical Specifications
• External Power Supply Voltage: 10-18 VDC
• Temperature: 30 to 60 degrees C 2. Operational Specifications
• Activity time out: 5 minutes
• Operating time on internal battery: minimum 10 hours
Figure A.6: PTS Handheld Remote Control with External Plug-In Charger
Controls
As shown in Figure A.7, all instrumentation was mounted in a large lockable, weatherproof NEMA 4 enclosure.
• Master power on-off switch,
• Raise/lower mast switch,
• Extend/retract signal arm switch,
• Battery voltmeter and cab light. The cab light was wired through the door switch to turn off when the control cab door was shut to conserve power, and
Appendix B: Survey of Practice
A survey of 19 different state Departments of Transportation (DOTs) was conducted during May and June 2014. The objective of the survey was to obtain an understanding of the practices followed in the various states regarding the use of PTS (referred to as temporary traffic signals in the survey), pilot car, and flagger operations. The survey was conducted via telephone or email depending on the preference of the state officials. The following section listed the questions used as a part of the survey followed by a summary of the survey responses for the various DOTs.
Q.1 Does the DOT use portable/temporary traffic signals in any of its work zones?
(a) If yes, does the DOT have any existing guidelines for the use of PTS in work zones with or without flaggers or does it follow the MUTCD guidelines only?
(b) If yes, was there a website with this information, or could you please email me a copy of the guidance?
Q.2 Does the DOT currently use any pilot car operations in any of the work zones? If yes, then what kind of work activity was expected to make use of them? (e.g., Overlay, bridge work, culvert replacement.)
Q.3 What was the average length (or minimum and maximum length) of work zones that use pilot car operations and temporary traffic signals in the state?
Q.4 Does the DOT consider ‘vehicle waiting time delays’ when it comes to the use of these devices? Have there been any experiences when excessive delay had been found by the use of pilot car operations?
(a) Was there a threshold on the hourly volumes or queue lengths when using these devices? Q.5 Was there a difference in guidance between the daytime and nighttime usage of pilot car or
temporary traffic signal operations? What was the DOT’s guidance for work on one-way work zone operations at night?
Arkansas State Highway and Transportation Department
The Arkansas State Highway and Transportation Department (AHTD) referred to the MUTCD guidelines and used the temporary traffic signals without flaggers in its work zones. The department used pilot car operations for bridge work, in long work zones of length greater than 1,000 feet, and during daytime operations. The temporary traffic signals were deployed on short work sections when both ends of work zones were visible to each other and could be used during daytime and nighttime operations. Interestingly, the department suggested that temporary traffic signals should not be used for road sections with very high volumes.
Connecticut Department of Transportation
The Connecticut Department of Transportation referred to the MUTCD guidelines for the use of temporary traffic signals. The department never makes use of the pilot car operations for any of its work zones. The temporary traffic signals were used for work zones of length less than 300 feet and the department believes that they could be used in work zones of longer lengths. The department used hourly volumes as a measure to determine the applicability of these devices and believes that an hourly volume of 700-800 vehicles in both directions would result in excessive delays. The department generally adopted a temporary traffic signal for night time operations with flagger controlled work zones and STOP signs.
Florida Department of Transportation
The Florida Department of Transportation rarely used the temporary traffic signals in its work zones and referred to the MUTCD guidelines if needed. The department used pilot car operations (referred to as rolling road block operations in Florida) in some of its work zones. Pilot cars were used for no more than 2 to 3 hours in one day in any work zone. Temporary traffic signals, if used, would be adopted for longer durations. The department preferred using the pilot car operations at nighttime and in the non-peak hours due to lower traffic volumes.
Idaho Transportation Department
The Idaho Transportation Department referred to its own standard set of guidelines for the use of the temporary traffic signals in its work zones. The department makes use of pilot car operations mostly for chip seal operations and work zones involving culvert replacement. The maximum length of work zones for the use of pilot car operations or the temporary traffic signals was about 5 miles. The department had a threshold of 15 minutes for the wait time when using a pilot car operation or the temporary traffic signal. For example, the work would begin with a 5 mile long work zone and subsequent decrease in the length of the work zone, until work was completed, which reduced the wait time. The department adopted the use of temporary traffic signals on the one-lane operations and preferred using it both day and nighttime. The department recommended the use of pilot car for daytime operations only.
Illinois Department of Transportation
The Illinois Department of Transportation referred to its own specifications for the use of temporary traffic signals and used the MUTCD as a supporting document. The department also does not adopt pilot car operations in any of its work zones. There was no maximum limit to the length of work zone that can make use of the temporary traffic signal, but in general the length varies from 250 feet to 1.5 miles. There was no threshold on the volumes that determine the use of the temporary traffic signal. The nine district offices made decisions pertaining to the use of the temporary traffic signal based on criteria such as the number of lanes available, the effects of addition of a signal on the volumes, and anticipated green times. The closure lengths were a major factor and if longer closure lengths were planned, the department recommended splitting the work to avoid long closure lengths. On the other hand, the long work zones were retained if the work zone was expected to serve lower volumes. The department had no difference in guidance for daytime and nighttime operations. Also, they did not have a preference in terms of duration of work zone for the use of temporary traffic signals.
Indiana Department of Transportation
The temporary traffic signal was not approved by the state of Indiana. The department made use of pilot car operation with police participation on a few projects of high importance and occasionally for nighttime operations. The length of work zone for the pilot car operations varied from 0.5 to 8 miles. The department considered a queue length of 1.5 miles to be significant and queues longer than this length were unacceptable. The volume threshold for pilot car operations on Interstates with only one lane open for traffic was 1,400 cars per hour and closure of two lanes simultaneously was discouraged for heavy volumes. The department adopts flagging for one-lane closures on rural roads.
Iowa Department of Transportation
The Iowa Department of Transportation referred to its own developmental standards for